Dental restoration processes, including replacing the missing tooth or teeth with permanent prostheses mounted on implants embedded in bony tissues of the upper and/or lower jaws, are well known. Fixed prostheses are fixed to the implant in a nominally permanent manner, and are not designed to be removed in the normal use thereof. These are to be contrasted with mobile or implant-supported prostheses, which are removable during normal use thereof and may or may not have an implant structure in the mouth. Both fixed and mobile permanent prostheses provide the appearance of teeth, and mimic the function thereof, allowing food to be masticated etc.
A number of different general procedures are known for implanting such fixed prostheses, and all start with embedding at least one implant, typically made from titanium or other medically compatible metal, in the bony tissues. Typically, one implant is required for each crown prosthesis, and at least two implants for bridge prostheses. In some cases requiring bridge prostheses, though, it may be possible to implant a prosthesis that is anchored at one retainer onto an implant, while at another retainer via a preparation, where there is sufficient healthy tooth left for this purpose.
One such general procedure, the conventional loading procedure, includes a surgical stage and a reconstruction stage. In the surgical stage, a suitable implant is first screwed or tapped into a surgically prepared site in the upper or lower jaw. Then, the gum tissue is closed over the implant, and the patent wears a denture during 3 to 6 months until the osseointegration process is completed, and the implant is firmly anchored in the jaw. During the healing period, the patient usually wears a denture over the closed gum. The denture includes a hard prosthesis that temporarily replaces the structure and function of the missing tooth or teeth, though it may include a softer portion that is adapted for fitting snugly over the gum. In the reconstruction stage part of the implant is exposed by removing a small amount of gum tissue, and a healing cup is mounted onto the implant, not in occlusion with the opposing dentition, and remains in place for a number of weeks until the gums have healed. The healing cup is not a prosthesis, but rather has a standard shape or form having a healing ring on a perimeter thereof that promotes healing of the gum tissue so that the prosthesis can eventually be mounted. The healing cup does not have the appearance of a dental structure, nor does it function as such—in fact this is considered highly undesirable. After this second healing period, the cup is removed, and the crown prosthesis is mounted to the implant, typically via a connecting structure.
This procedure has the advantage of substantially preventing any loading directly onto the implant until this has been firmly anchored onto the bone via osseointegration. The dentures themselves do not directly load the implant, but rather transmit loads to the jaws in a substantially diffused manner. However, the healing cup itself is unsightly and may have an undesirable psychological effect of self-consciousness on many patients. The procedure for a bridge prosthesis is similar to that described above, but carried out on one or both anchoring sites, according to the number of implants that are required.
In a variation of the conventional loading procedure, the permanent prosthesis is attached in a second surgical procedure that takes place some time later than the 3 to 6 month healing period.
A second general procedure, known as the one step procedure (also as “immediate restoration”), is similar to the conventional loading procedure described above, but is a shorter procedure in which the step of closing the gums at the beginning of the osseointegration period is omitted. Accordingly, rather than surgically closing the gum over the implant, a suitable healing cup is instead mounted on the implant immediately, the cup not being in occlusion with the opposing dentition. Thus, healing of the gum tissue is concurrent with osseointegration of the implant. However, this type of procedure, though shorter than the conventional loading procedure and reducing the number of surgical interventions with respect thereto, carries potential risks of infection and of micromovement of the implant due to loads that may be applied to the healing cup when masticating, for example. Further, the esthetically unappealing cup is visible for a considerable period.
A third general procedure, known as immediate loading, is similar to the one step procedure, but is actually even shorter, wherein rather than providing a healing cup for the healing and osseointegration stage, a first prosthesis is mounted to the implant within 2 days after the implant is embedded in the jaw, in occlusion with the opposing dentition, and is used for mastication and so on. In some cases, this prosthesis may be mounted to the implant via a temporary connecting structure that promotes healing of the gum, and this connecting structure may be replaced at a later stage with a permanent connector, together with a second, permanent prosthesis. While a shorter process than the one-step procedure, and while not involving the use of an unsightly healing cup, there is nevertheless a risk of infection, as well as of substantial micromovement of the implant, as the first prosthesis is directly loaded by the regular forces in the intraoral cavity, such as mastication for example, before the implant has been fully anchored in place.
In a variation of the immediate loading procedure, known as the early loading procedure, the first prosthesis is installed after 2 days from installation of the implant, but before 3 months have elapsed.
Another type of procedure is disclosed in U.S. Pat. No. 5,906,489. An implant is disclosed therein for supporting a hard prosthesis that is used for chewing, and includes a base sheet that has a longitudinal axis and a lateral axis. At least two holes extend through the base sheet. A post is connected to the base sheet. The temporary dental implant is installed over a patient's jaw bone by exposing the jaw bone by displacing covering tissue. The base sheet is shaped into a U-shape so that the legs of the U-shape are directed away from the post. The shaped base sheet is installed over the jaw bone by securing the covering tissue to the jaw bone and loading the prosthesis onto the post. The prosthesis is loaded a few days after the temporary implant has been installed, after which the prosthesis is used for chewing.